Academic Chemistry
Thermochemistry Test Review
Energy (in general)
1)
ÿ ÿ;"ÿ
U-, ,ÿ
" ÿ' ' t: -k:ÿ,.
(energy
due to motion) &
: I ,<"
ÿ
There are two types ofÿenergy:
"<7 t.} 4ÿ
I{,I'L "i I ;;'i.,l ÿ ÿ'
ÿ9ÿIi i!"0ÿ
(energy due to position). Thermal energy (heat) is
kinetic/potential (circle one). Chemical energy (energy stored in bonds) is kinetic/potential (circle one).
< !!i:
2)
Define the Law of Coqservation of Mass: ......... ÿ:ÿ
3)
A toaster is powered with 1500 J of electric energy. When on, it converts 1000 J to thermal energy, 300 J to light energy,
and the remaining portion to sound energy. How much sound energy is produced?
"v
<
Enthalpy
4)
t
........................
In your body, blood is at a higher temperature than any other body tissue. So when your hands are cold, how does your
:ÿ
body warm them up?
always travels from ÿto
5)
,
', :i:ÿ.<.. )ÿ,ÿ ,iÿ:
ÿ: ' ÿ :' '
because heat
iects.
What is the heat change for the above reaction, at constan$ pressure if ypu begin with 282.6 g of K20? Is this
endothermic or exothermic?
-,
' i '";"" : :'" 'ÿ4"
<°
ÿ'
'":"ii"i ,"
AH = 215 k]
.... .'( K20 (s) +'.' H20 (I) "-ÿ,i 2KOH (aq)
""
<;J° Y < I
'- '
....
Z
........
{.,..!ÿ ° ,:"
O, D" "'ÿ
&H=
6) What is the heat of reaction for the following: CÿHs(g) -> CÿHs(I) + 41.8 kJ
Energy Diagrams
_ -
7)
__
The energy diagram below represents the equatig£: 2No(g) + 02(g) )-> 2NO2(g).
products, activation energy
a) Label thereactants,
"ÿ'
'ÿ.
i
c
w
(' b) Is the reaction endothermic ore-xoi:hermÿcT).,.:._.__ _
..
<
#
c
£
n
c) Explain the energy transfer (Which form of energy existed first, and to which
kind °fenergyldidl it change?) ÿ:< 'ÿ '" ÿ .... " ' ' ......I"
Reaction Progress
d) Would AH be positive or(negative?)
.:ÿ, ,,, .., . ,,., <,:,
24
i
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.ÿ¢Chemistry
Unit 14
/
• //
,reakinÿ bonds -.- --¢eauires/releases (chose one) energy and would therefore be an exotherm ¢/endothermic)(choose one)
process.
Use the diagram below to answer the following questions:
iiÿil,a)
>,
What is value of the change in enthalpy? ...... ii"i - ÿ ÿI
What letter represents this change? __
b3
b==
O
b) Is this process endothermic or exothermic? t"ÿ; .)%
LU
3
c) Which letter represents the heat required to break bonds? !)ÿi/'
D
What is this called? {"!ÿ (' t ÿ, , ÿ,,
A
o
n
d) Which letter represents the activation energy of the reverse
reaction?
e) Which letter represents the enthalpy of the reactants?
Reaction Coordinate
Which letter represents the enthalpy of the products?
>
C1-].ÿ(g) + 202@-ÿ CO2(g) + 211ÿO({i:I + S%,4 kJ !'
Heat of Formation
Cor questions 10-12: (a) Calculate the standard enthalpy of the reaction for the following reactions using the standard
,,-nthalpies of formation chart in the back of the packet or the other information given in the problem, (b) classify each as either
endothermic or exothermic, and (c) determine which energy diagram best describes the reaction:
Energy Diagram 3:
Energy Diagram 2:
Energy Diagram 1:
C+D
C
PE
(kJ)
Progress oflhe reaction
roÿFess
oÿ-ess
10) 4NH3(g) + 502(g) "-) 6H20(g) + 4NO(g)
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>
e /
',
c) Diagram #ÿ
25
Academic Chemistry
11) Si02(g) + 3C (s) ¢ 624.710 "ÿ SiC (s) + 2C0 (g)
z ÿ
c) Diagram #ÿ>ÿ
12)Magnesium reacts with hydrochloric acid in a single replacement reaction.
Balanced Equation:
.,', .;:. ? i
a)
t
b) ': " : ÿ
c) Diagram # !_
Specific Heat
:13) Define specific heat capacity: .k\ÿ\ÿ;ÿ -.ÿ:,: ,, \>,.Vvÿt ÿ:ÿ<{i" /i"ÿO ÿ.;ÿ,ÿ, ÿ':ÿA>d', t.(.,,.ÿ
f'
tÿ
st
14) The 2.ÿ,ÿ+ .'ÿ 'ÿ1" ÿ?-'ÿ'
that the specific heat capacity, the more resistant the object is to a change in temperature (i.e.
it requires more energy to change the temperature),£Jÿ
t<" \"
tÿ ÿ,0
(7.ÿ{ ¢ ,
,
i( ÿ
-
l.[,
, ,
!I
' ,+' ÿ'i
15) Determine the initial temperature bf an 84.ÿ gram sample of water after 14,500 J of heat is applied. The final temperature
of the water sample is 100 -°C. The specific heat of water is 4.18 Jlg-°C.
+<
26
)#i.Chemistryÿ
Unit 14
• A sample ofÿis placed in a hot water bath with an initial temperature of 415.0 ÿ-C causing
3.50 x 103 J of heat to be transferred, After several minutes the temperature of the water was recorded at 22.0 -°C.
Calculate the mass of the copper sample.
\
Specific Heat I
Copper
0.385 J/g x°C
Aluminum
0.902 J/g x°C
17) Using the specific heat data from above, will aluminum or copper reach the higher temperature assuming they gain the
same amount of heat?
.._{ÿI)ÿ<ÿIÿSÿ.
ÿALÿio ÿ_L -ÿ,ÿ (:
,ÿ(ÿf'ÿ f, <ÿ' /)/ÿ. ÿ ÿ' ÿ,,
Phase Changes
18) How much heat is required to change 32.5 grams ice into steam, from -10°C to 115°C?
Specific heat of water = 4.18 J/g.°C
Specific heat of steam = 1.97 J/g.°C
AHfusion = 334 J/g
Specific heat of ice = 2.03 J/g."C
iÿ
"
ÿ:ÿJ- 'ÿ
....
AHvaporlzaÿion
2259+J/g
'
,=
<:i#
......+'>
ÿJ ?k -'+ÿ'+1"
.......
/ , ) >
, "
"'t,
'
+
Ho ('#fYV f ,
Calorimetw
....
,
"t, ,,-
....
':::7 J
19)A solution's temperature increases as the frequency of collisions between reactants increases. ............
Temperature is a measure of the molecules'
\ ',, t t ÿ ÿ' ÿt,L, s'
energy.
20)According to the law of conservation of energy, heat !0St by the reaction in a calorimeter must
';-
the heat 9aifl-edklost (chose one) by the water,
......
+'ÿ,,D
C:!,/4ÿ Oÿ f ':ÿ'
21) Students conduct an experiment where a reaction occurs in a calorimeter. Calculate the heat released
in Joules to the nearest whole number. The specific heat capacity of water is 4.184 J/g°C.
I
Mass
l:nitial
: "
-Final :: :ÿ
(g-) ',! Temperature(°C)` Temperature (oc),i
100.0
25.0
32.0
, s\
, [ /
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t
\,': ÿf i
• ("1
'1
, ' {
L
,' )
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